1. Field of the Invention
The present invention relates to a frame interpolation apparatus for generating interpolated frames between base frames and inserting them between the base frames.
2. Description of the Related Art
Recent years have seen the practical application of techniques to generate smoother moving images free of much image lag by increasing the number of image frames using frame interpolation technology. For example, a technology in practical use is such that moving images of 60 frames per second (60 Hz) are converted into moving images of 120 Hz for display at a doubled speed.
In Japan, the one-segment broadcasting started in April 2006. The so-called “One Seg” (one-segment) broadcasting is a broadcasting using narrow bands intended mainly for the receiving by mobile devices such as mobile phones. In One Seg broadcasting, the images are normally transmitted at 15 frames per second (15 Hz), so that there is greater necessity for increase in the number of frames. With a general One Seg decoder, video image output is made at a frame frequency of 60 Hz, so that basically four frames of the same video image are outputted. In this case, a frame interpolation apparatus for increasing the number of frames of moving images using the aforementioned frame interpolation technology is connected in a position subsequent to the One Seg decoder.
There is a technology proposed for such a frame interpolation apparatus, in which the number of frame repetitions is continuously counted to detect any change in the succession, and when the result of detection is not a four-frame succession, the interpolation processing is halted or the sampling frame is shifted.
In the above-mentioned technology, the sampling frame is changed whenever a change in the number of input frame repetitions occurs, and as a result the sampling rate becomes variable. If there is an error in detecting the number of frame repetitions due to low detection accuracy of frame repetitions (for example, the detection determines the absence of a change point despite its actual presence in the input video image), there will be a failure to sample the video image. Under such circumstances, cases may arise where the input images are not reflected in the output images.
Also, the images to be inputted to the frame interpolation apparatus may not only be ones for One Seg broadcasting, but may sometimes be ones with clock OSD (On-Screen Display) or touch panel OSD superposed thereon. Then, as a result of counting frame repetitions, there may be cases where the number of repetitions is judged to be 1, 2, or 3, for instance, depending on the effect of OSD. In this case, a problem arises where the actual number of repetitions of one-segment video image cannot be detected correctly. In such a case, if the sampling point is shifted at variable sampling rate, processings of large bandwidths may sometimes overlap with each other in the computation of frame interpolation in a pipeline process. And this may present possibilities of a rising peak of bandwidth of SDRAM (Synchronous Dynamic Random Access Memory). Further, the then video images at the frame interpolation output may lose the smoothness which is otherwise preset.
Even though the number of repetitions of one-segment video image except for OSD is detected, another problem arises where the clock in OSD remains stopped or unchanged while the actual time elapses, when the sampling frame is variable. This is because when the sampling frame is variable and, for instance, the clock OSD is superposed on a stopped one-segment video image, no sampling is effected unless any change occurs in the one-segment video image.